Thyrotropin (TSH) is the pituitary glycoprotein hormone which controls the growth and function of the thyroid gland. It is produced solely by thyrotrope cells, one of five terminally differentiated pituitary cell types. The TSH molecule is composed two non-identical glycosylated subunits, alpha and TSHbeta, which are con-covalently associated. These two subunits arise independently from separate genes located on different chromosomes. The alpha-subunit is expressed not only in TSH cells but also in pituitary gonadotropes and placental cells. In contrast, TSHbeta gene expression is restricted only to thyrotropes. The studies proposed in this grant are a direct extension of our important previous contributions in which the murine TSHbeta gene was identified and sequenced, its promoter region characterized, the important functional cis-acting DNA elements determine, and important transcription factors bindings to these regions identified. Two of these transcription factors are Pit-1 and GATA-2 which interact in a unique complex on the TSHbeta promoter. Our propose studies are designed to precisely define the molecular basis for the observed synergistic interaction of Pit-1 and GATA-2. We will first map the respective sites on Pit-1 and GATA-2 that are responsible for their interaction, their DNA binding, and their ability to functionally synergize. We will precisely define the spatial and orientation requirements of their binding sites on the TSHbeta promoter. To establish the physiological in vivo role of the Pit-1/GATA-2 interaction, we will develop unique cell culture and transgenic models of targeted aberrant GATA-2 function and determine its effect on endogenous TSHbeta gene expression. These projects will utilize the most modern techniques of molecular and cell biology incorporated into cell culture and transgenic technology. These studies will provide new fundamental knowledge on the structural interactions between different classes of transcription factors and the impact of these interactions on normal physiology.